1. Field of the Invention
The present invention relates to a method and apparatus for issuing repair alerts for various mechanical components assembled in an electric injection molding machine, and more particularly, to a method and apparatus for issuing repair alerts which automatically execute diagnostic processing to determine the need for repair without requiring action by a worker in charge of operation of the electric injection molding machine.
2. Description of the Related Art
Common electric injection molding machines can use servomotors, for example, AC servomotors instead of hydraulic drives. Generally, a rotary drive of the servomotor is applied to a rotation direct-transmission mechanism, in which a nut and a ball screw are combined, through a pulley and a timing belt, thereby shortening the entire length of the injection molding machine to achieve space saving for installation.
The operating condition of such an electric injection molding machine varies depending on an individual user. For an electric injection molding machine having a high operation rate, the period between inspections needs to be short, that is, the frequency of inspection needs to be high. Under such circumstances, a worker spends much time taking direct measurements during inspections, and even more time processing the measured data to predict when a repair may be needed.
Particularly, with regard to inspection of timing belts, which are arranged dispersedly, the worker needs to compare tension measured using a tension meter and that of the initial state from values or visually from graphical values, listening to noise generated by the machine and inferring from experience, or the like for each timing belt.
Recently, a portable sound wave type belt tension meter capable of measuring the tension of a timing belt with sound waves has been provided to facilitate the measurement of the tension to some extent (refer to, for example, pamphlet of sound wave type belt tension U-507, 5000 sheets issued by Gates Unitta Asia on Apr. 13, 2004).
In the above-described conventional method, which captures change over time of components in the drive force transmitting mechanism of the servomotor, the issuance of repair alerts is not executed automatically. This is because a worker is always needed. Only a skilled person can determine such a change since a portion of the inspection depends on visual check or acoustic sense. It takes more time to perform such a procedure. Furthermore, there may be a difference in the outcome of the inspection as it depends on the individual person performing the inspection and evaluating the outcome.
In another conventional method, vibration is applied to a structure body of a machine with a vibration exciter and its vibration waveform is detected at other portions of the structure with a sensor so as to analyze the characteristic of the vibration by waveform analysis. Such a method exaggerates the measurement work itself including setting the vibration exciter and arranging a sensor. Furthermore, analysis of cause-and-effect relationship in the vibration is not easy.
Recently, a fast Fourier-converting method has been proposed. In the method, a signal from an encoder is converted by fast Fourier transform by applying white noise for gain adjustment of the servosystem in a numerical control machine tool (refer to, for example, Jpn. Pat. Appln. KOKAI Publication No. 2001-175303).
The white noise principally contains all the frequency components. Each frequency component has substantially the same amplitude. Any conventional white noise generator can be used.
As described above, the method, which captures change overtime of components in the drive force transmitting mechanism of the servomotor, does not allow the repair alert to be issued easily. This is because a worker is always needed. In addition, only a skilled person can determine such a change since a portion of the inspection depends on visual check or acoustic sense. Such inspection procedure takes time, and there may be a difference in the outcome of the inspection depending on the individual person evaluating the outcome.